This invention relates to batteries.
Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized; the cathode contains or consumes an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a sheet-like layer, typically called the separator.
When a battery is used as an electrical energy source in a device, such as a hearing aid or a cellular telephone, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
In a metal-air electrochemical cell, the cathode structure contains a material that can catalyze the reduction of oxygen, which enters the cell as a component of atmospheric air passing through access ports in the container. Zinc oxide or zincate is formed in the anode. Thus, the overall electrochemical reaction within the cell results in zinc metal being oxidized to zinc ions and oxygen from the air being reduced to hydroxyl ions. While these chemical reactions are taking place, electrons are transferred from the anode to the cathode, providing power to the device.
The invention relates to a method of making a cathode assembly for a metal-air battery. The method includes extruding a composition having a catalyst, a fibrillatable material, and a lubricant, to form an extrudate; calendering the extrudate; connecting the extrudate to a current collector; and heating the extrudate to remove at least a portion of the lubricant to make the cathode assembly. The method can further include laminating a separator to the cathode assembly.
The method can be used to produce a thin, strong, and self-supporting cathode. The cathode can be made uniform to provide reliable battery performance. The cathode is flexible, allowing the cathode to be formed in different shapes.
The preferred catalyst is manganese oxide. The preferred fibrillatable material is polytetrafluoroethylene. The preferred lubricant is an iso-paraffinic solvent.
The extrusion can be performed, for example, by ram extrusion or screw extrusion, at less than room temperature or greater than room temperature. Extruding the composition fibrillates the fibrillatable material to produce a strong cathode assembly.
Calendering of the extrudate can include passing the extrudate between rollers at a temperature greater than room temperature. The rollers can be moving at the same speed or at different speeds, for example, at a speed differential of 1.05-1.20:1, to produce a cathode with asymmetrical hardness. Calendering the extrudate produces a thin and uniform cathode that provides reliable battery performance. A thin cathode allows more active material (e.g., anode material) to be placed in the battery, thereby increasing the battery""s capacity.
The extrudate can be connected to the current collector by embedding the current collector to the extrudate such that the thickness of the extrudate can remain substantially unchanged after being embedded with the current collector. Embedding the current collector to the extrudate can be performed by pressing the current collector and the extrudate between rollers.
The extrudate can be heated after lamination. Heating of the extrudate can remove substantially all of the lubricant from the extrudate.
In another aspect, the invention relates to a method of making a cathode for a metal-air battery including extruding a composition having a catalyst, a fibrillatable material, and a lubricant, to form an extrudate; calendering the extrudate between rollers; and pressing the extrudate to a current collector between rollers. The method can further include heating the extrudate to remove at least a portion of the lubricant.
In another aspect, the invention relates to a method of making a metal-air battery. The method includes making a cathode assembly by extruding a composition having a catalyst, a fibrillatable material, and a lubricant, to form an extrudate; calendering the extrudate; connecting the extrudate to a current collector; and heating the extrudate to remove at least a portion of the lubricant to make the cathode assembly; placing the cathode assembly in a housing comprising air access openings such that air entering the housing contacts the cathode assembly; placing a separator adjacent to the cathode assembly; and placing an anode adjacent to the separator. The anode can include zinc. The catalyst can include manganese oxide.
Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.